1. Field of the Invention
This invention relates to a randomly dumped tower packing element for use in gas or vapor-liquid mass transfer towers and, more particularly, to a tower packing element that accommodates distillation, gas absorption, stripping, and other related operations.
2. Description of the Prior Art
Randomly dumped beds of packing elements are typically employed in towers with gas or vapor phase entering the packed bed from the bottom of the tower and rising upwardly for a vertical tower. Liquid is administered to the top of the packed bed and runs through the packed bed down to the bottom.
The packing elements which make up the packed bed function to provide a "skeleton" in the tower over the surface of which liquor is passed in the form of a thin film and preferably turbulent films. The skeleton is open to allow the gas or vapor to rise upwardly. As the vapor passes over the thin film of liquid present on the packing elements, mass transfer occurs between the gas or vapor phases and the liquid phase.
It is well known in the art that the efficiency and the rate of mass transfer per unit volume of the packed bed is dependent upon the surface area which the packing bed can provide.
Different configurations of packing elements are known to increase the surface area of the packing bed in a consistent manner. U.S. Pat. No. 4,376,081 discloses a randomly dumped tower packing element formed from strip material having the shape of a two dimensional continuously progressing curve (e.g. a sine or cosine curve) which is rotated between 10.degree. and 180.degree. to form a partial ring. The packing element configuration provides a longitudinal curvature as a result of its rotation, but the resulting shape also displays the characteristic curve of the continuously progressing curve itself. The packing element includes slots with tongues depending from the slots to provide more accessibility to the available surface area. The tongues point in any direction and from any portion of the surface.
Another important feature in the efficiency of tower packing elements is the extent to which their surfaces come into direct contact with each other. Direct contact between elements provides convenient flow paths along which the descending liquid can pass, instead of falling all the way through the packed bed.
U.S. Pat. No. 4,327,043 discloses randomly dumped tower packing elements formed of strip material having an open-ended bent configuration made up of three interconnected curved zones. An intermediate, concave curved portion is flanked on either side by oppositely curved convex end portions. Each of these portions has slots formed therein and tongues which depend from each slot. The tongues all point toward the inside of the intermediate curved portion. This unsymmetrical configuration provides a highly randomized packed bed which enhances internal liquid distribution and mass transfer performance.
U.S. Pat. No. 5,200,119 discloses a packing element formed of at least two substantially straight legs tangentially attached to the ends of an arcuately bent surface. The straight leg portions of the element contain slots. Depending from these slots are tongues which project transversely away from the surface of the element. The arcuately bent surface does not contain slots or tongues in order to maximize the beneficial turbulence obtained when the fluid contacts the smooth surface of the bend.
The prior art packing elements suffer a number of deficiencies mostly due to the lack of consistent uniformity in which the elements form the packed bed and the way in which these elements settle over time. The geometric shape of the elements not only effects the available surface area and the direct contact each element has with adjoining elements, but also the stability of the packed bed and the consistency with which the desired characteristics are obtained. Due to non-accessibility of certain regions of packed beds to gas-liquid flows, fluid maldistributions result. Thus certain portions of the packing are rendered less accessible to efficient liquid gas contact than other portions with the result that the overall mass transfer efficiency of the packing is impaired.
While a number of geometric configurations have been proposed for increasing the efficiency of tower packing elements, there is a need for a randomly dumped packing element having a geometric configuration which increases the statistical uniformity of the randomly dumped layers. The tower packing element should have a substantially increased surface area available for liquid film formation and enhancing the probability of direct contact between adjacent packing elements in the tower.